1. Field of the Invention
This invention relates generally to camera modules and relates more specifically to camera modules having a movable lens barrel and wherein the actuators are deployed in a way to achieve minimal size of the camera module.
2. Description of the Prior Art
Digital camera modules are used with many electronic devices such as e.g. mobile phones, personal data assistants (PDAs), computers, etc. These camera modules have to be as small as possible, reliable, and easy to be used, robust and require minimal power consumption. Furthermore the design of the camera modules should allow low manufacturing cost, while the quality of the images has to conform to a high standard.
Therefore modern camera modules should allow auto-focusing and minimal friction of the bearing for a movable lens barrel in order to achieve precise focusing of the camera.
It is important that the camera modules, which are to be built in mobile electronic devices as e.g. mobile phones, require minimal size. It is a challenge for the designers of camera modules to develop auto-focus camera modules having a reliable drive for moving a lens barrel having minimal size and consuming minimal power.
Solutions dealing with the design of cameras and related auto-focus drives are described in following patents:
U.S. Patent (U.S. Pat. No. 7,400,068 to Tseng) teaches a voice coil motor apparatus applied to an auto-focus or variable-focus lens module of a miniaturized camera including: a voice coil motor, a plurality of steel guidance shafts, a lens holder, and a base. The voice coil motor also includes a magnetic part including magnets and yokes, and an electrical part including a coil winding. The magnetic part is rigidly coupled to the lens holder to form the moving member. The electrical part and the steel guidance shafts are fixed on the base to form the non-moving member. The pre-loaded force due to the interaction between the leakage flux of the magnetic part and the steel guidance shafts eliminates the free-play resulting from the tolerance gap between the moving and the non-moving members, and that the magnets and the yokes form a non-circular magnetic structure having a rectangular contour in order to minimize the overall dimension.
U.S. Patent (U.S. Pat. No. 4,873,542 to Nakayama) discloses an auto-focus camera having a focusing lens supporting feed screw rod supported substantially parallel to the lens optical axis and having a slit for focusing at its one end, and a spacer nut meshed with a feed screw portion of the feed screw rod, so that is longitudinal movement is prevented, and rotated by the focus control motor.
U.S. Patent (U.S. Pat. No. 4,783,676 to Aihara et al.) discloses a lens drive device for a camera driving a lens by a motor to a position preset by an operator. The lens position is stored in a memory. When the lens is to be moved to the stored position while the lens is moved by an auto-focus device to an in-focus position, the lens is instantly moved by the motor to the stored position based on the data stored in the memory.